Thin film transistor liquid crystal display (TFT-LCD) dominates current flat screen display market due to characteristics such as small volume, low power consumption and no radiation and so on. TFT-LCD is formed by cell assembling an array substrate and a color filter substrate. In the array substrate, gate scanning lines and data signal lines are arranged to cross each other to define pixel regions, and pixel electrodes and the thin film transistors are arranged in respective pixel regions.
Bright lines and bright spots are major defects occurred during current TFT-LCD fabricating process. The bright lines are presented as lines with bright colors on the display panel which do not vary with the color change on the screen. The bright lines are caused largely by the breakage of the gate scanning lines or data signal lines due to the dusts. The bright spots are caused by various reasons such as dusts, thin film residues etc. For 4 mask technology, the two major defects are gray tone bridging and channel breakage which are bright spots defects caused by a-Si under-etch and a-Si over-etch respectively in the channel region. It is difficult to detect these two kinds of defects during fabricating process. The gray tone bridging can not be detected until a testing stage of the array substrate; whereas the channel breakage can not even be detected during the testing stage of the array substrate, if the channel is not completely broken and the charging and discharging function can still work. In this case, it can only be detected, evident as a mura later in a testing stage of the liquid crystal cell.
In view of the above, all the above defects can only be detected in the testing stage of array substrate at earliest, and some channel breakage defects can not be detected until the testing stage of the liquid crystal cell. This could cause a delay in adjusting the apparatus, so that similar defects would continue to occur in a large batch of products.